RFID carrier sensing method and RFID system using this RFID carrier sensing method

• US 8,531,271 B2
• Filed: 07/27/2007
• Issued: 09/10/2013
• Est. Priority Date: 01/31/2005
• Status: Expired due to Fees

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Tanaka, Yoshinori
• Primary Examiner(s): Zimmerman, Brian
• Assistant Examiner(s): Khan, Omer S
• Application Number:
  US11/878,925
• Publication Number:
  US 20070279193A1
• Time in Patent Office: 2,237 Days
• Field of Search: 340/10.1, 340/10.2, 340/10.3, 370/334, 370/335, 370/336, 370/337, 370/338, 370/339, 370/340, 370/341, 370/342, 370/343, 370/344
• US Class Current: 340/10.1
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: G06K 7/10356 using a plurality of antennas, e.g. configurations including means to resolve interference between the plurality of antennas
• CPC Class Codes: H04B 7/10 Polarisation diversity; Directional diversity

Abstract

An RFID system that is capable of increasing the probability of a spare channel being detected and reducing the influence of interference between reader/writers comprises: a reader/writer which has a reader/writer main body section and an antenna capable of polarization switching, and which sends a continuous carrier wave; and a tag which uses tag information to modulate the continuous carrier wave and sends back a response signal to the reader/writer. The reader/writer main body section judges the level of a received interference signal and determines a channel and polarization direction for which the level of the interference signal is equal to or less than a threshold value, and receives a response signal from the tag on the determined channel and in the polarization direction.

Claims

1. An RFID system, comprising:

a reader/writer which has a controller section and a plurality of antennae each with characteristic polarization, and which sends a continuous carrier wave; and

a tag which uses tag information to modulate the continuous carrier wave and sends back a response signal to the reader/writer, wherein

the controller section judges prior to send the continuous carrier wave, the level of the interference signal received from another reader/writer by switching each of the plurality of antennae for each of the plurality of channels and determines a channel and antenna for which the judged level of the interference signal is equal to or less than the threshold value, and receives a response signal from the tag by means of the determined antenna via the determined channel,

wherein the channels are the respective bands of a frequency band that has been divided into a plurality of bandwidths.

2. The RFID system according to claim 1, wherein the tag is constituted by a patch antenna and an LSI which is connected in parallel to the patch antenna and which has an interface section having a capacitance component that resonates with the inductance component.

3. A carrier sensing method of an RFID system which has a reader/writer that has a-controller section and a plurality of antennae each set with a different polarization direction, and which sends a continuous carrier wave, and a tag which uses tag information to modulate the continuous carrier wave and sends back a response signal to the reader/writer,

the method comprising the steps of:

in the reader/writer,

sequentially measuring prior to send the continuous carrier wave, an interference signal level received from another reader/writer by switching each of the plurality of antennae for each of the plurality of channels;

measuring the interference signal level by switching the specified channel to another channel when the interference signal level to be measured is equal to or more than the threshold value;

determining an antenna set to a channel and polarization direction for which the interference signal level thus measured does not exceed the threshold value; and

setting to receive the response signal from the tag using the determined channel and antenna,

wherein the channels are the respective bands of a frequency band that has been divided into a plurality of bandwidths.

4. The RFID system according to claim 3, wherein the tag is constituted by a patch antenna and an LSI which is connected in parallel to the patch antenna and has an interface section having a capacitance component that resonates with the inductance component.